As in a conventional frequencymeter or phasemeter, it serves to reconstitute respectively the frequency or the phase of the signal to be evaluated, and to provide an indication of the accuracy with which these parameters are measured together with items for determining the quality of the signal (e.g. signal/noise ratio, form factor).
The signal analysis methods commonly used for measuring frequency and phase are generally based either:
on analog processing and filtering methods for performing integration or counting zero crossings, with the duration of the integration or the filtering being a function of the desired accuracy or;
on methods for locking an oscillator, for example by means of a phase lock loop, thereby isolating the signal to be measured so that measurements can then be performed thereon; or else;
directly on the signal from the locked oscillator, or on the control signals thereof.
The use of these methods suffers from the drawback of not storing the results of earlier processing. As a result, any parameter value estimated from one portion of the signal, is actually made use of in processing a different portion of the signal subsequent to the portion which was used for obtaining the initial estimate, and this has unfortunate consequences both:
on performance, since this technique cannot provide the best possible adaptation to variability in the parameters, and as a result it is more sensitive to disturbing signals (noise, interferring spectrum lines) superposed on the signals to be measured; and also
on complexity, since when using the above-described techniques, it is very difficult to provide optimum adaptation at each of the stages that need to be implemented in order to achieve the desired aim. In particular, the stages of acquisition and of tracking require different characteristics, so they either require separate devices, or else they require the characteristics of a set of analog circuits to be adapted to each of these stages, and thus without excessive complication, it is very difficult for the measuring device to be optimally adapted and give best results for each of these stages.
Further, when performing successive estimates of the same parameter, it is not possible to use the same signal. The results of successive estimates are thus performed over signal periods taken successively in time, which makes it essential to use hypotheses which are guaranteed to provide valid and reproducible results.
The object of the present invention is to mitigate these drawbacks.